As humans conquered the globe, these parasitic hitchhikers went along for the ride. Past work had studied the genetics of lice, but relied on DNA that passes on from the maternal line, making it difficult to get a complete picture of human migration. [Tiny & Nasty: Images of Things That Make Us Sick]

Toward that end, Marina Ascunce, an entomologist at the Florida Museum of Natural History Museum, and her colleagues analyzed nuclear DNA, genetic material that is passed on from both male and female lice, in 75 specimen from 10 sites across four regions: Asia, North America, Central America, and Europe. They also collected clothing lice from people in Nepal and Canada.

Past migration

They found that lice from Honduras closely resembled Asian lice.

"Lice from Honduras may have been brought by the first people in America, and that's why we see this closer genetic affinity," Ascunce told LiveScience.

By contrast, lice from New York were more closely related to European parasites, likely reflecting North America's waves of European colonization over the centuries, Ascunce said.

In addition, because there is not much gene flow between different lice populations, insecticides could be more effective if they target genetic vulnerabilities specific to local populations, she said.

While the study is preliminary, a more thorough sampling of worldwide lice could provide insight into why head lice differ from clothing lice, which harbor in clothing and can spread deadly diseases.

Genetic analysis could also reveal when and where humans interbred with Neanderthals and other archaic hominid species, the researchers write in the paper.